Devices that can treat tissue non-invasively are extensively used to treat numerous diverse skin conditions. Among other uses, non-invasive energy delivery devices may be used to tighten loose skin to make a patient appear younger, remove skin spots or hair, or kill bacteria. Such non-invasive energy delivery devices emit electromagnetic energy in different regions of the electromagnetic spectrum for tissue treatment.
High frequency treatment devices, such as radio-frequency (RF)-based devices, may be used to treat skin tissue non-ablatively and non-invasively by passing high frequency energy through a surface of the skin to underlying tissue, while actively cooling the skin to prevent damage to a region of the tissue near the skin surface. The high frequency energy heats the tissue beneath the cooled region to a temperature sufficient to denature collagen, which causes the collagen to contract and shrink and, thereby, tighten the treated tissue. Treatment with high frequency energy also causes a mild inflammation. The inflammatory response of the treated tissue causes new collagen to be generated over time (typically, between three days and six months following treatment), which results in further tissue contraction.
Modern high frequency treatment devices employ a high frequency generator and treatment tips having electrodes coupled with the high frequency generator. Conventional electrodes consist of a pattern of metallic features carried on a flexible electrically insulating substrate, such as a thin film of polyimide. The temperature of the treatment tip is measured by temperature sensors, such as thermistors or thermocouples, carried on the treatment tip.
Among other purposes, the output of the temperature sensors is used for closed-loop control of coolant application and/or detecting aberrant skin temperatures as a safety precaution. Specifically, the non-patient side of the electrode in the treatment tip may be sprayed with a coolant or cryogen spray under feedback control of the temperature sensors for cooling the tissue region proximate to the skin surface. The controller triggers the coolant spray based upon an evaluation of the temperature readings from the temperature sensors.
Treatment tips exhibit dimensional restrictions established by power constraints of the high frequency generator. Consequently, the surface area of the electrode carried by the treatment tip is constrained at least in part by the electrical load imposed on the high frequency generator. This size restriction on the electrode limits the rate or speed by which the treatment tip can be used to conduct a procedure on a patient.
What is needed, therefore, are apparatus and methods for treating skin conditions that deliver high frequency energy over a larger surface area than possible using conventional treatment tips, as well as overcoming other deficiencies of conventional treatment tips.